<!DOCTYPE html>
<html lang="cn">
<head>
    <meta charset="UTF-8">
    <title>二级菜单</title>
    <style type="text/css">
        .menu > li {
            display: inline-block;
            position: relative;
            padding: 0 20px 0 20px;
        }

        li > ol {
            display: none;
        }

        .menu > li:hover > ol {
            display: block;
            position: absolute;
            width: 100px;
            left: -20px;
        }

        li {
            list-style-type: none;
        }
    </style>
</head>
<body>
<ol class="menu">
    <li>
        <a>一级菜单</a>
        <ol>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
        </ol>
    </li>
    <li>
        <a>一级菜单</a>
        <ol>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
        </ol>
    </li>
    <li>
        <a>一级菜单</a>
        <ol>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
            <li>二级菜单</li>
        </ol>
    </li>
</ol>
</body>
</html>